Infectious conjunctivitis is an ophthalmic disorder characterized by inflammation of the conjunctiva secondary to invasion of a microbe. Microbes capable of causing conjunctivitis in humans include bacteria (including Mycobacteria sp), viruses, fungi, or amoebae. Current treatment for bacterial conjunctivitis consists of antibiotic drops. Because antibiotic drops are ineffective against viral conjunctivitis, treatment of such infections consists only of relieving symptoms. Treatments for fungi and amoeba conjunctivitis consist of a small selection of medications which lacks anti-bacterial or anti-viral activity and which, in addition, is toxic to the ocular surface.
Diagnosis of the various causative agents such as bacteria, virus, or fungus, in infectious conjunctivitis is not economically feasible because accurate diagnosis requires sophisticated laboratory culture not easily integrated into the average healthcare practice. Because accurate diagnosis is impractical, most conjunctivitis is presumed to be bacterial without culturing and is treated with antibiotics. Antibiotic treatment is suboptimal because it is ineffective against viral or fungal conjunctivitis.
The use of steroids is approached cautiously in the setting of ocular infection. While steroids can have the benefit of reducing the severity of the inflammation in an acute infection, they are also known to increase susceptibility to certain infections.
Topical corticosteroids are routinely used to control ocular inflammation. Their mechanism of action involves the inhibition of the immune response and the subsequent tissue destruction that exuberant inflammation may cause. Corticosteroid has the undesirable side effect of limiting the body's intrinsic ability to fight infection. In fact, inopportune steroids usage can worsen the course of an infection secondary to mycobacteria, virus, or fungus. Thus, the use of a combined antimicrobial-steroid medication in ocular infections is recommended only under careful observation of a trained ophthalmologist because of these significant risks. In fact, Tobradex® (Alcon), the most commonly prescribed combination ophthalmic antimicrobial-steroid drug, specifically lists ‘viral disease of the cornea and conjunctiva, mycobacteria infection, and fungal infection’ as absolute contraindications to its use. Clearly, these combination drugs were not intended to be used in the face of infectious conjunctivitis in which bacterial infection cannot be confirmed.
In summary, there is currently no ophthalmic antimicrobial drug with broad activity against all the causes of conjunctivitis or keratitis, and there is currently no approved antimicrobial/steroid, or antimicrobial/non steroidal anti-inflammatory combination drug that can be safely used in infectious conjunctivitis or keratitis that can potentially be viral or fungal in origin.